This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The actin cytoskeleton near the protruding cell edge consists of two kinetically, kinematically, molecularly, and materially distinct networks. Only one of the two, which we refer to as the lamellipodium, has the properties of an Arp2/3-controlled, dendritically branched and treadmilling network. The second network, referred to as the lamella, does contain Arp2/3 as well, but its polymerization is largely independent of Arp2/3 activity. We hypothesize that the assembly of F-actin in the lamella is mediated by formins and tropomyosin. The aim of this project is to implement a Virtual Cell (VC) model of F-actin network assembly at the leading edge to predict the differential kinetics of simultaneous Arp2/3- and formin-mediated lamellipodium and lamella formation.